md5加密解密

import java.security.*;   
import java.security.spec.*;   
  
class MD5_test {   
 public final static String MD5(String s) {   
  char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',   
    'a', 'b', 'c', 'd', 'e', 'f' };   
  try {   
   byte[] strTemp = s.getBytes();   
   MessageDigest mdTemp = MessageDigest.getInstance("MD5");   
   mdTemp.update(strTemp);   
   byte[] md = mdTemp.digest();   
   int j = md.length;   
   char str[] = new char[j * 2];   
   int k = 0;   
   for (int i = 0; i < j; i++) {   
    byte byte0 = md[i];   
    str[k++] = hexDigits[byte0 >>> 4 & 0xf];   
    str[k++] = hexDigits[byte0 & 0xf];   
   }   
   return new String(str);   
  } catch (Exception e) {   
   return null;   
  }   
 }   
  
 public static void main(String[] args) {   
  // MD5_Test aa = new MD5_Test();   
  System.out.print(MD5_test.MD5("b"));   
 }   
}  

   

Java代码 
import java.security.MessageDigest;   
  
  
public class MD5andKL {   
 // MD5加码。32位   
 public static String MD5(String inStr) {   
  MessageDigest md5 = null;   
  try {   
   md5 = MessageDigest.getInstance("MD5");   
  } catch (Exception e) {   
   System.out.println(e.toString());   
   e.printStackTrace();   
   return "";   
  }   
  char[] charArray = inStr.toCharArray();   
  byte[] byteArray = new byte[charArray.length];   
  
  for (int i = 0; i < charArray.length; i++)   
   byteArray[i] = (byte) charArray[i];   
  
  byte[] md5Bytes = md5.digest(byteArray);   
  
  StringBuffer hexValue = new StringBuffer();   
  
  for (int i = 0; i < md5Bytes.length; i++) {   
   int val = ((int) md5Bytes[i]) & 0xff;   
   if (val < 16)   
    hexValue.append("0");   
   hexValue.append(Integer.toHexString(val));   
  }   
  
  return hexValue.toString();   
 }   
  
 // 可逆的加密算法   
 public static String KL(String inStr) {   
  // String s = new String(inStr);   
  char[] a = inStr.toCharArray();   
  for (int i = 0; i < a.length; i++) {   
   a[i] = (char) (a[i] ^ 't');   
  }   
  String s = new String(a);   
  return s;   
 }   
  
 // 加密后解密   
 public static String JM(String inStr) {   
  char[] a = inStr.toCharArray();   
  for (int i = 0; i < a.length; i++) {   
   a[i] = (char) (a[i] ^ 't');   
  }   
  String k = new String(a);   
  return k;   
 }   
    
 // 测试主函数   
 public static void main(String args[]) {   
  String s = new String("a");   
  System.out.println("原始：" + s);   
  System.out.println("MD5后：" + MD5(s));   
  System.out.println("MD5后再加密：" + KL(MD5(s)));   
  System.out.println("解密为MD5后的：" + JM(KL(MD5(s))));   
 }   
}